The Oakland Athletics purchased León's contract before the start of the 2008 minor league season, and he was assigned to the Advanced-A Stockton Ports. He made 20 relief appearances for Stockton in 2008, posting a 2.86 ERA and 28 strikeouts in 281⁄3 innings. León was assigned back to Saltillo on June 24, 2008, and played the rest of the minor league season there, going 2–1 with a 4.30 ERA in 13 games. He again played winter ball with the Tomateros de Culiacán, pitching 201⁄3 innings over 23 relief appearances.[1]
In 2009, León was assigned to the Double-AMidland RockHounds for the entire minor league season. In 33 appearances, 7 of which were starts, he would post a 2–3 win–loss, 3.51 ERA, and 63 strikeouts in a then career-high 741⁄3 innings pitched.[1] For the third consecutive season, León returned to the Mexican winter league, and pitched to a 2–0 record with a 4.15 ERA in 23 appearances.[1] In 2010, he would pitch in 3 games for Midland before being placed on the disabled list, and would then undergo Tommy John surgery that would sideline him for the rest of the season.[2] Having recovered from surgery, León made 5 starts for the Arizona League Athletics in 2011, posting an 8.53 ERA in 61⁄3 innings.[1] He began the 2012 season with Stockton, later being promoted to Double-A Midland and the Triple-ASacramento River Cats. In 44 total appearances, León would post a 4–1 win–loss record, 2.70 ERA, and 74 strikeouts in 662⁄3 innings.[1]
León played for the Mexico national baseball team in the 2013 World Baseball Classic. In a first-round game against the Canada national baseball team, he started a brawl after hitting Rene Tosoni with a pitch following a buntsingle by Chris Robinson.[2][3] León was converted into a full-time starter during the 2013 minor league season, which he split between Double-A and Triple-A. In 25 total starts, he pitched to a 9–8 record, 4.12 ERA, and 97 strikeouts in 144 total innings.[1] León played the entire 2014 season with Triple-A Sacramento, posting a 10–7 record, 4.97 ERA, and 128 strikeouts in 145 innings pitched.[1] He was briefly promoted to the major leagues in May 2014, but returned to Triple-A without having made his MLB debut.[2]
León made his MLB debut on April 22, 2015, through he would spend the majority of the season with the Nashville Sounds, which became Oakland's Triple-A affiliate following the 2014 season. In 20 appearances for Nashville, León pitched to a 2–5 record, 2.95 ERA, and 55 strikeouts.[1] In 19 relief appearances for Oakland, León would post a 0–2 record, 4.39 ERA, and 19 strikeouts.[4]
Toronto Blue Jays
On January 5, 2016, León was traded to the Toronto Blue Jays for cash considerations or a player to be named later.[5] On March 30, John Gibbons announced that León had made the Opening Day roster, and would pitch out of the bullpen.[6] He was designated for assignment on April 13.[7] León cleared waivers on April 23, and was outrighted to the Triple-A Buffalo Bisons.[8]
Samsung Lions
On May 18, 2016, Leon was acquired by the Samsung Lions of the KBO League and signed to a one-year, $500,000 contract.[9]
León was traded to the Leones de Yucatán of the Mexican League on August 13, 2018. León did not play in a game in 2020 due to the cancellation of the Mexican League season because of the COVID-19 pandemic.[10]
